<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /*resize*/
    body,
    div,
    dl,
    dt,
    dd,
    ul,
    ol,
    li,
    h1,
    h2,
    h3,
    h4,
    h5,
    h6,
    form,
    input,
    textarea,
    p,
    th,
    td,
    menu {
      margin: 0;
      padding: 0;
    }

    body {
      font-size: 12px;
      -webkit-text-size-adjust: none;
      font-family: Arial, Helvetica, sans-serif;
    }

    img {
      border: none;
    }

    ol,
    ul {
      list-style: none;
    }

    em {
      font-style: normal;
    }

    a {
      text-decoration: none;
    }

    .clearfix {
      #zoom: 1;
    }

    .clearfix:after {
      content: ' ';
      display: block;
      height: 0;
      clear: both;
      color: #fff;
    }

    body {
      background: #333;
    }

    .breathe-btn {
      position: relative;
      width: 100px;
      height: 10px;
      margin: 40px auto;
      line-height: 40px;
      border: 1px solid #2b92d4;
      border-radius: 5px;
      color: #fff;
      font-size: 20px;
      text-align: center;
      cursor: pointer;
      box-shadow: 0 1px 2px rgba(0, 0, 0, .3);
      overflow: hidden;
      background-image: -webkit-gradient(linear, left top, left bottom, from(#6cc3fe), to(#21a1d0));
      -webkit-animation-timing-function: ease-in-out;
      -webkit-animation-name: breathe;
      -webkit-animation-duration: 2700ms;
      -webkit-animation-iteration-count: infinite;
      -webkit-animation-direction: alternate;
    }

    @-webkit-keyframes breathe {
      0% {
        opacity: .2;
        box-shadow: 0 1px 2px rgba(255, 255, 255, 0.1);
      }

      100% {
        opacity: 1;
        border: 1px solid rgba(59, 235, 235, 1);
        box-shadow: 0 1px 30px rgba(59, 255, 255, 1);
      }
    }
  </style>
</head>

<body>
  <div class="breathe-btn"></div>
</body>

</html>